Solvent blends for ethylene copolymers

ABSTRACT

A solvent blend capable of dissolving at a temperature of at least 60° C. copolymers of ethylene and ethylenically unsaturated carboxylic acid. The solvent blend comprises from about 5 to about 35 percent by weight of an acyclic alcohol having from 2 to 12 carbon atoms, based upon the total weight of said solvent blend, about 3 percent to about 90 percent by weight of a monocyclic aromatic hydrocarbon, based upon the total weight of said solvent blend, and from about 5 to about 92 percent by weight of a halogenated C 2  hydrocarbon, based on the total weight of said solvent blend. An exemplary solvent blend contains about 10 percent by weight of isopropanol, about 80 percent by weight of perchloroethylene, and about 10 percent by weight of toluene, based on the total weight of the solvent blend.

BACKGROUND OF THE INVENTION

This invention relates to solvents for ethylene copolymers. In oneaspect, this invention relates to solvent blends for copolymers ofethylene and ethylenically unsaturated carboxylic acid. In anotheraspect, this invention pertains to solvent blends which will hold suchcopolymers in solution at a temperature of about 60° C.

Copolymers of ethylene and ethylenically unsaturated carboxylic acid arewell known, and a number of such copolymers are commercially available.Further, such copolymers are characterized, among other things, by theiroutstanding adhesion to a variety of metallic and non-metallicsubstrates, outstanding toughness and tensile strength. Because of theseunique properties, such copolymers find commercial utility, amongothers, in packaging, building products, communications andtransportation end use applications. It has been found that a mostimportant property of such copolymers is their adhesive characteristics.Thus, such copolymers are used widely as adhesive for laminating two ormore substrates into a laminate. In a dry film lamination technique, thecopolymers are first converted into dry adhesive films then placedbetween two substrates to form an intimate bond under heat and pressure.In an extrusion lamination technique, a molten coating of copolymer isextruded into a nip of two substrates to form a laminate. In an adhesivelamination technique, a solution or an aqueous dispersion of copolymeris first coated unto a substrate using a roll coater. The solvent orwater is then dried off and the dried, coated substrate comes in contactwith another substrate under pressure to form a laminate. When anadhesive lamination technique is involved, it is important to have aneffective solvent system for copolymers. More specifically, an effectivesolvent system is needed to dissolve the copolymer in an adhesivesolution. Still another need is an effective solvent system capable ofcleaning applicator rolls (e.g. gravure rolls) and other laminatingequipment which handles copolymer solutions or dispersions at anelevated temperature.

Tachi et al. (Kogyo Kagaku Zasshi 73(2), 398-42 (1970)) discloses thesolubility of ethylene/acrylic acid copolymers in organic solvents,including mixed solvents. Tetrahydrofuran and certain mixed solvents(e.g. cyclohexane and dioxane) can dissolve the copolymer at 60° C.However, none of these single solvents or mixtures suggest the ternarysolvent blends of the present invention. German OLS No. 2,814,030discloses a solution of graft ethylene acrylic acid at elevatedtemperatures in organic solvents such as cyclohexane to prepare"suspensions" of fine (insoluble) particles at cooler temperatures.Cyclohexane at an elevated temperature is used. There is no suggestionof the ternary solvent blends of the present invention. U.S. Pat. No.3,711,456 discloses a method for the preparation of ethylene carboxylicacid polymers having improved optical properties. Such polymers areobtained by intimately contacting a normally solid random copolymer witha "polyethylene" solvent at elevated temperature, and thereafterseparating the solvent from the solid ethylene polymer. The lowmolecular weight crystalline, low acrylic acid portion of the ethylenecarboxylic acid copolymer is selectively extracted at elevatedtemperatures. Only single solvents are used. U.S. Pat. No. 3,814,737discloses the use xylene/acetic acid and xylene/isopropanol as solventmixtures for ethylene carboxylic acid copolymers at elevatedtemperatures. The temperature involved exceeds 100° C. Further, binarysolvent mixtures are used. U.S. Pat. No. 3,554,957 discloses a solventsystem for copolymers of ethylene and acrylic acid which will maintainthe copolymer in solution at substantially normal room temperature. Thesolvent system comprises between about 55 and about 65 percent by weighttoluene, based upon the total weight of the solvent blend, and betweenabout 35 and about 45 percent by weight tetrahydrofuran, based upon thetotal weight of the solvent blend. The copolymer can be dissolved andheld in solution at normal room temperature in amounts up to about 5percent by weight based upon the total weight of the solution. However,the solvent system of this patent is ecologically "unclean."

Accordingly, it is an object of this invention to provide a solventsystem for copolymers of ethylene and ethylenically unsaturatedcarboxylic acid which is effective at a temperature of about 60° C.Another object of this invention is to provide a solvent system which isecologically "clean." It is yet another object of this invention toprovide a solution containing a dissolved copolymer of ethylene andethylenically unsaturated carboxylic acid which can be applied ordeposited at a temperature of 60° C. Other objects and advantages of theinvention will become apparent in the following description.

SUMMARY OF THE INVENTION

The objects of this invention are obtained by a solvent blend capable ofdissolving at a temperature of 60° C. a copolymer of ethylene andethylenically unsaturated carboxylic acid having from about 2.5 to about30 percent by weight of said carboxylic acid based upon the total weightof said copolymer. The solvent blend comprises from about 5 to about 35percent by weight of an acyclic alcohol having from 2 to 12 carbonatoms, based upon the total weight of said solvent blend, about 3percent to about 90 percent by weight of a monocyclic aromatichydrocarbon, based upon the total weight of said solvent blend, and fromabout 5 to about 92 percent by weight of a halogenated C₂ hydrocarbon,based on the total weight of said solvent blend.

The term "soluble or dissolving" as used herein means a solvent blendhaving a solubility rating of 2 or less as defined in Table I.

DETAILED DESCRIPTION AND EMBODIMENTS

The polymer which is beneficially used in accordance with this inventionis a normally solid thermoplastic polymer of ethylene modified bymonomers having reactive carboxylic acid groups, particularly acopolymer or a major proportion of ethylene and a minor proportion,typically from 2.5 to 30 percent, preferably 3 to 20 percent by weight,of an ethylenically unsaturated carboxylic acid, and an ionic metal saltthereof commonly known as an "ionomer." Specific examples of suchsuitable ethylenically unsaturated carboxylic acids (which term includesmono- and polybasic acids, acid anhydrides, and partial esters ofpolybasic acids) are acrylic acid, methacrylic acid, crotonic acid,fumaric acid, maleic acid, itaconic acid, maleic anhydride, monomethylmaleate, monoethyl maleate, monomethyl fumarate, monoethyl fumarate,tripropylene glycol monomethyl ether acid maleate, or ethylene glycolmonophenyl ether acid maleate. The carboxylic acid monomer is preferablyselected from α,β-ethylenically unsaturated mono- and polycarboxylicacids and acid anhydrides having from 3 to 8 carbon atoms per moleculeand partial esters of such polycarboxylic acid wherein the acid moietyhas at least one carboxylic acid group and the alcohol moiety has from 1to 20 carbon atoms. The copolymer may consist essentially of ethyleneand one or more of such ethylenically unsaturated acid comonomers or canalso contain small amounts of other monomer copolymerizable withethylene. Thus, the copolymer can contain other copolymerizable monomersincluding an ester of acrylic acid. Methods of making such copolymer arereadily known in the art.

The term "ionomer" as used herein means a copolymer of ethylene andethylenically unsaturated carboxylic acid cross-linked with a metal ion.Na, Ca, Zn or another similar metal may be used. Ionomers arecommercially available and methods of their manufacture are readilyknown in the art.

The alcohols used in connection with the present invention are acyclicalcohols having from 2 to 12 carbon atoms. Such alcohols may have eitherstraight chain or branch chain carbon backbones. Alcohols having from 2to 5 carbon atoms are particularly preferred. The alcohols mayconstitute from about 5 to about 35 percent by weight, preferably fromabout 7 to about 20 percent by weight, and most preferably from about 7to about 15 percent by weight of the total weight of the solvents.

Monoacyclic aromatic hydrocarbons used in connection with the presentinvention may constitute at least 3 percent by weight of the totalweight of the solvents. Toluenes and xylenes are particularly preferred.

The halogenated C₂ hydrocarbons of the present invention may constituteat least 5 percent by weight of the total weight of solvents.1,1,1-Trichloroethane and perchloroethylene are particularly preferred.

The copolymers of the present invention can be dissolved in the solventsystem described herein above and the resultant solution can be appliedto various substrates using well known coating techniques as an adhesiveor as a protective coating.

The solvent blends of the present invention are useful at a temperatureof at least 60° C.; their utility is further enhanced at temperatureshigher than 60° C.

The specific working examples that follow are intended to illustrate theinvention but not to be construed as limiting its scope. In theexamples, parts and percentages are by weight unless otherwise specifiedor required by the context.

EXAMPLE 1

Fifty grams of a ternary solvent blend consisting of1,1,1-trichloroethane, isopropanol and toluene were prepared at variousratios shown in Table II in a two-ounce glass bottle. 2.5 Grams of anethylene acrylic acid copolymer acrylic acid concentration: 20.5 percentby weight; melt index: 236 dg/min.) were added to the glass bottle. Thebottle was tightly sealed with a Saran-lined cap and placed in a waterbath maintained at a temperature of 60° C. The samples were vigorouslyagitated by hand for a period of about 10 seconds at five minuteintervals for a period of about one hour. Each bottle was then rated at60° C. in accordance with the rating scale in Table I.

                  TABLE I                                                         ______________________________________                                        Solubility Rating Scale                                                       Rating                                                                              Remarks                                                                 ______________________________________                                        1     Water white, no visible haze under ambient lighting                           conditions, no gels or particulates.                                    2     Clear, but with detectable haze; may also be water                            white (No. 1) but with some gels.                                       3     Homogenous, but very hazy; almost translucent to                              opaque; may or may not have gel.                                        4     Nonhomogenous, two phases; one usually clear, the                             other viscous and opaque; no undissolved beads.                         5     Little or no effect; beads may be partially attacked                          or swollen, but are essentially intact.                                 ______________________________________                                    

                  TABLE II                                                        ______________________________________                                        Trichloroethane/Isopropanol/Toluene Blend                                           Trichloro-                                                              Test  ethane    Isopropanol                                                                              Toluene Solubility                                 No.   (% by wt.)                                                                              (% by wt.) (% by wt.)                                                                            Ratings                                    ______________________________________                                        2-1   15        15         70      1                                          2-2   70        15         15      1                                           2-3* 25        50         25      4                                          2-4   90        5          5       2                                          ______________________________________                                         *Not an example of this invention                                        

EXAMPLE 2

The procedure of Example 1 was repeated with another ternary solventblend consisting of perchloroethylene, isopropanol and toluene. Theresults are shown in Table III.

                  TABLE III                                                       ______________________________________                                               Perchloro-                                                             Test   ethylene Isopropanol                                                                              Toluene Solubility                                 No.    (% by wt.)                                                                             (% by wt.) (% by wt.)                                                                            Rating                                     ______________________________________                                        3-1   90        7          3       1                                          3-2   10        10         80      1                                          3-3   40        20         40      1                                          3-4   45        35         20      1                                          3-5   10        10         80      1                                          ______________________________________                                    

EXAMPLE 3

The procedure of Example 1 was repeated with another ternary solventblend consisting of trichloroethane, isopropanol, xylene. Solubilityrating is shown in Table IV.

                  TABLE IV                                                        ______________________________________                                        Trichloroethane/Isopropanol/Xylene Blend                                            Trichloro-                                                              Test  ethane    Isopropanol                                                                              Xylene  Solubility                                 No.   (% by wt.)                                                                              (% by wt.) (% by wt.)                                                                            Rating                                     ______________________________________                                        4-1   10        15         75      1                                          4-2   80        10         10      1                                          ______________________________________                                    

EXAMPLE 4

The procedure of Example 1 is repeated with another ternary solventblend consisting of trichloroethane, ethanol, and toluene. Thesolubility rating is shown in Table V.

                  TABLE V                                                         ______________________________________                                              Trichloro-                                                              Test  ethane     Ethanol    Toluene  Solubility                               No.   (% by wt.) (% by wt.) (% by wt.)                                                                             Rating                                   ______________________________________                                        5-1   10         15         75       2                                        5-2   40         20         40       2                                        5-3   80         10         10       2                                        ______________________________________                                    

EXAMPLE 5

The procedure of Example 1 was repeated with another ternary solventblend consisting of perchloroethylene, isobutanol, toluene. Thesolubility ratings are shown in Table VI.

                  TABLE VI                                                        ______________________________________                                              Perchloro-                                                              Test  ethylene   Isobutanol Toluene  Solubility                               No.   (% by wt.) (% by wt.) (% by wt.)                                                                             Rating                                   ______________________________________                                        6-1   80         10         10       1                                        6-2   15         10         75       1                                        6-3   5          5          90       1                                         6-4* 25         50         25       4                                        ______________________________________                                         *Not an example of this invention                                        

EXAMPLE 6

The procedure of Example 1 was repeated with another ternary solventblend consisting of perchloroethylene, n-propanol, and toluene. Thesolubility rating is shown in Table VII.

                  TABLE VII                                                       ______________________________________                                              Perchloro-                                                              Test  ethylene   n-propanol Toluene  Solubility                               No.   (% by wt.) (% by wt.) (% by wt.)                                                                             Rating                                   ______________________________________                                        7-1   80         10         10       2                                        7-2   10         10         80       1                                        ______________________________________                                    

EXAMPLE 7

The procedure of Example 1 was repeated with another ternary solventblend consisting of methylene chloride, isopropanol and toluene. Thesolubility rating is shown in Table VIII.

                  TABLE VIII                                                      ______________________________________                                              Methylene                                                               Test  Chloride   Isopropanol Toluene  Solubility                              No.   (% by wt.) (% by wt.)  (% by wt.)                                                                             Rating                                  ______________________________________                                        8-1   10         10          80       1                                       8-2   50         10          40       2                                       ______________________________________                                    

EXAMPLE 8

The procedure of Example 1 was repeated with another ternary solventblend consisting of perchloroethylene, t-butyl alcohol, and toluene. Thesolubility rating is shown in Table IX.

                  TABLE IX                                                        ______________________________________                                              Perchloro-                                                              Test  ethylene   t-Butanol  Toluene  Solubility                               No.   (% by wt.) (% by wt.) (% by wt.)                                                                             Rating                                   ______________________________________                                        9-1   90         5          5        1                                        9-2   5          5          90       1                                        9-3   40         20         40       1                                        ______________________________________                                    

EXAMPLE 9

The procedure of Example 1 was repeated with another ternary solventblend consisting of 80 percent by weight of perchloroethylene, 10% byweight of isopropanol and 10% by weight of toluene, based on the totalweight of the solvent blend. In place of ethylene acrylic acidcopolymer, various Surlyn® ionomers were used as indicated in Table X.

                  TABLE X                                                         ______________________________________                                        Solubility of Ionomers                                                                   Melt      Metal     Solubility                                     Ionomer    Index     ion       Rating @ 60° C.                         ______________________________________                                        Surlyn®  1706                                                                        0.7       Zn        2                                              Surlyn®  1650                                                                        1.4       Zn        2                                              Surlyn® 1652                                                                         5.0       Zn        2                                              Surlyn® 1702                                                                         14.0      Zn        2                                              Surlyn® 1707                                                                         0.9       Na        1                                              Surlyn® 1555                                                                         10.0      Na        1                                              ______________________________________                                    

EXAMPLE 10

The procedure of Example 1 was repeated with a ternary solvent blendconsisting of 15 percent by weight of trichloroethane/15% by weight ofisopropanol/70% by weight of toluene. However various ethylene acrylicacid copolymers shown in Table XI was used.

                  TABLE XI                                                        ______________________________________                                               Amount of                                                              Test   Acrylic Acid           Solubility                                      No.    (% by wt.)  Melt Index Rating @ 60° C.                          ______________________________________                                        11.1   2.7         --         1                                               11.2   3.5          11        1                                               11.3   8.0          9         1                                               11.4   10.7        --         1                                               11.5   14.8        412        1                                               11.6   16.3        412        1                                               11.7   18.0        274        1                                               11.8   20.5        236        1                                               11.9   22.3        308        1                                               11.10  26.6        426        1                                               ______________________________________                                    

As shown in Examples 1-9, the ternary solvent blends of the presentinvention are effective in dissolving ethylene acrylic acid copolymersat a temperature of at least 60° C.

Table XI shows that the solvent blends of the present invention areeffective at a temperature of at least 60° C. for ethylene acrylic acidcopolymers having from about 2.7 to about 27 percent by weight ofacrylic acid content.

In place of the particular solvent blends and copolymers used in thepreceding examples, there can be used other solvent blends and ethylenecarboxylic acid copolymers as hereinbefore described with substantiallysimilar results.

While certain representative embodiments have been shown in detail forthe purposes of illustrating the invention, it will be apparent to thoseskilled in the art that various changes and modifications can be madewithout departing from the spirit and scope of the present invention.

What is claimed is:
 1. A solution comprising a solvent blend whichcomprises from about 5 to about 35 percent by weight of an acyclicalcohol selected from the group consisting of ethanol, propanol,isopropanol, n-butanol, isobutanol and t-butanol, based upon the totalweight of said solvent blend, about 3 percent to about 90 percent byweight of a monocyclic aromatic hydrocarbon, based upon the total weightof said solvent blend, and from about 5 to about 92 percent by weight ofa halogenated C₂ hydrocarbon, based upon the total weight of saidsolvent blend, and a copolymer of ethylene and ethylenically unsaturatedcarboxylic acid, or an ionic metal salt thereof, having from about 2.5to about 30 percent by weight of said carboxylic acid, based on thetotal weight of said copolymer, characterized in that said copolymerremains dissolved at a temperature of at least 60° C.
 2. A solutionaccording to claim 1 wherein said copolymer is a random copolymer ofethylene and acrylic acid.
 3. A solution according to claim 1 whereinsaid copolymer is cross-linked with a Na or Zn ion.
 4. A solutionaccording to claim 1 wherein said monocyclic aromatic hydrocarbon isbenzene, toluene, or xylene.
 5. A solution according to claim 1 whereinsaid halogenated C₂ hydrocarbon is 1,1,1-trichloroethane orperchloroethylene.
 6. A solution comprising a solvent blend whichcomprises about 7 percent by weight of isopropanol, about 90 percent byweight of perchloroethylene, and about 3 percent by weight of toluene,based on the total weight of said solvent blend, and a copolymer orethylene and ethylenically unsaturated carboxylic acid having from about2.5 to about 30 percent by weight of said carboxylic acid, based on thetotal weight of said copolymer, characterized in that said copolymerremains dissolved at a temperature of at least 60° C.
 7. A solutioncomprising a solvent blend which comprises about 5 percent by weight oftertiary butyl alcohol, about 90 percent by weight of perchloroethylene,and about 5 percent by weight of toluene, based on the total weight ofsaid solvent blend, and a copolymer of ethylene and ethylenicallyunsaturated carboxylic acid having from about 2.5 to about 30 percent byweight of said carboxylic acid, based on the total weight of saidcopolymer, characterized in that said copolymer remains dissolved at atemperature of at least 60° C.
 8. A solution comprising a solvent blendwhich comprises about 10 percent by weight of isopropanol, about 10percent by weight of perchloroethylene, and about 80 percent by weightof toluene, based on the total weight of said solvent blend, and acopolymer of ethylene and ethylenically unsaturated carboxylic acidhaving from about 2.5 to about 30 percent by weight of said carboxylicacid, based on the total weight of said copolymer, characterized in thatsaid copolymer remains dissolved at a temperature of at least 60° C. 9.A solution according to claim 6, 7 or 8 wherein said copolymer is arandom copolymer of ethylene and acrylic acid.